1. Field of the Invention
The present invention relates to an optical system-driving device provided in an image-reading apparatus such as electrostatic photographic copying machine, facsimile and image scanner.
2. Description of the Prior Art
For example, in an optical system movement-type electrostatic photographic copying machine, one motor is used as a driving source and this motor is always rotated in one direction to convey a transfer paper and move an optical system during the copying.
And, in such the electrostatic photographic copying machine, a so-called one side driving-type optical system-driving device, in which a carriage with an optical member, such as a light source and a mirror, placed thereon is slidably held by a support rod put in said carriage at one end side in a direction meeting at right angles with a moving direction thereof, the other end side being slidably supported by a carriage-supporting member, and said one end side being driven, has been adopted in many cases. In addition, a rotation of the motor is transmitted to a driving pulley through a regular rotation electro-magnetic clutch or a reverse electro-magnetic clutch. That is to say, said regular rotation electro-magnetic clutch is switched on to regularly rotate said driving pulley through the regular rotation electro-magnetic clutch, whereby moving an optical system in a scanning direction, during the scanning of a manuscript while the driving pulley is reversed through said reverse electro-magnetic clutch when said optical system is returned to the home position.
However, in the case where said carriage-supporting rod is put in the carriage with some allowance and the regular rotation electro-magnetic clutch is started, the carriage is vibrated with a sudden start thereof and thus the optical system is vibrated to vibrate said light source, said mirror and the like. As a result, a strain is produced in an image according to circumstances.
So, a device, in which a voltage applied to a regular rotation electro-magnetic clutch is gradually risen by a time-constant of CR in a driving circuit of said regular rotation electro-magnetic clutch to reduce a vibration at a starting time, has been made.
It is, however, difficult to finely regulate said time-constant, so that said sudden start can not be perfectly avoided and accordingly said vibration can not be perfectly eliminated at present.